1. Field of the Invention:
The present invention relates to apparatus and processes for packaging microelectronic dice. In particular, the present invention relates to a packaging technology that fabricates build-up layers on an encapsulated microelectronic die and on the encapsulation material which covers the microelectronic die.
2. State of the Art:
Higher performance, lower cost, increased miniaturization of integrated circuit components, and greater packaging density of integrated circuits are ongoing goals of the computer industry. As these goals are achieved, microelectronic dice become smaller. Of course, the goal of greater packaging density requires that the entire microelectronic die package be equal to or only slightly larger (about 10% to 30%) than the size of the microelectronic die itself. Such microelectronic die packaging is called a "chip scale packaging" or "CSP".
As shown in FIG. 8, true CSP would involve fabricating build-up layers directly on an active surface 204 of a microelectronic die 202. The build-up layers may include a dielectric layer 206 disposed on the microelectronic die active surface 204. Conductive traces 208 may be formed on the dielectric layer 206, wherein a portion of each conductive trace 208 contacts at least one contact 212 on the microelectronic die active surface 204. External contacts, such as solder balls or conductive pins for contact with an external component (not shown), may be fabricated to electrically contact at least one conductive trace 208. FIG. 8 illustrates the external contacts as solder balls 214 where are surrounded by a solder mask material 216 on the dielectric layer 206. However in such true CSP, the surface area provided by the microelectronic die active surface 204 generally does not provide enough surface for all of the external contacts needed to contact the external component (not shown).
Additional surface area can be provided through the use of an interposer, such a substrate (substantially rigid material) or a flex component (substantially flexible material). FIG. 9 illustrates a substrate interposer 222 having a microelectronic die 224 attached to and in electrical contact with a first surface 226 of the substrate interposer 222 through small solder balls 228. The small solder balls 228 extend between contacts 232 on the microelectronic die 224 and conductive traces 234 on the substrate interposer first surface 226. The conductive traces 234 are in discrete electrical contact with bond pads 236 on a second surface 238 of the substrate interposer 222 through vias 242 that extend through the substrate interposer 222. External contacts are formed on the bond pads 236 (shown as solder balls 244).
The use of the substrate interposer 222 requires number of processing steps. These processing steps increase the cost of the package. Additionally, even the use of the small solder balls 228 presents crowding problems which can result in shorting between the small solder balls 228 and can present difficulties in inserting underfilling between the microelectronic die 224 and the substrate interposer 222 to prevent contamination.
FIG. 10 illustrates a flex component interposer 252 wherein an active surface 254 of a microelectronic die 256 is attached to a first surface 258 of the flex component interposer 252 with a layer of adhesive 262. The microelectronic die 256 is encapsulated in an encapsulation material 264. Openings are formed in the flex component interposer 252 by laser abalation through the flex component interposer 252 to contacts 266 on the microelectronic die active surface 254 and to selected metal pads 268 residing within the flex component interposer 252. A conductive material layer is formed over a second surface 272 of the flex component interposer 252 and in the openings. The conductive material layer is patterned with standard photomask/etch processes to form conductive vias 274 and conductive traces 276. External contacts are formed on the conductive traces 276 (shown as solder balls 278 surrounded by a solder mask material 282 proximate the conductive traces 276).
The use of a flex component interposer 252 requires gluing material layers which form the flex component interposer 252 and requires gluing the flex component interposer 252 to the microelectronic die 256. These gluing processes are relatively difficult and increase the cost of the package.
Therefore, it would be advantageous to develop new apparatus and techniques to provide additional surface area to form traces for use in CSP applications, while utilizing commercially available, widely practiced semiconductor fabrication techniques.